1. Field of the Invention
This invention relates to acetabular prostheses having a socket bearing and a cup wherein the bearing is retained within the cup by means of a self-locking taper. The bearing is composed of a non-plastic material, such as a metal or a ceramic, which will not exhibit substantial flow when used in an acetabular prosthesis.
2. Description of the Prior Art
Acetabular prostheses having metal socket bearings are known in the art. Early constructions are shown in Sivash, U.S. Pat. Nos. 3,820,167, 3,943,576, and 4,077,070, and Noiles, U.S. Pat. No. 3,848,272, and U.S. Pat. No. Re 28,895. These prostheses were of the constrained type wherein the bearing encompassed more than half of the ball. The bearing consisted of two pieces which were placed around the ball and secured to the cup by riveting or screw threads. Because of the difficulty of assembling the prosthesis in situ, the surgeon was provided with an assembled joint comprising both the femoral and acetabular components.
PCT Patent Publication No. WO 83/02555 shows a variation of these earlier constructions wherein the metal bearing could encompass 180.degree. or less of the femoral ball. Attachment between the bearing and the cup was again by means of a screw thread. Accordingly, although in situ assembly was not impossible, it was still generally impractical because of the screw thread.
Noiles, U.S. Pat. No. 4,678,472, shows two metal bearing constructions. In the first construction (FIGS. 9-10 of the '472 patent), the bearing comprises two pieces which encompass more than half of the ball and which are held together around the ball by means of retaining ring 74. For this construction, in the assembled joint, the bearing can rotate within the cup to provide a greater range of motion for the joint. In the second construction (FIGS. 33-34 of the '472 patent), the bearing again comprises two parts which in this case are locked in place within the cup by wedge 136.
Other constructions for acetabular prostheses employing metal socket bearings are disclosed in Frey et al., U.S. Pat. No. 4,969,910.
A bearing composed of a ceramic material is disclosed in Mittelmeier et al., U.S. Pat. No. 3,894,297. In this case, the bearing is carried by a plastic casing, with the bearing being held in the casing by a flexible, circumferential bead, and with the casing being held in the prosthesis' cup by a circumferential bead formed just inside of the rim of the cup.